How to Test and Replace the Thermistor in a Samsung Dishwasher

The thermistor (temperature sensor) in a Samsung dishwasher monitors water temperature and tells the control board when to activate and deactivate the heating element. When the thermistor fails, the board receives incorrect temperature readings and either shuts down the heater prematurely (resulting in cold wash water and error code 5E) or fails to turn the heater off (potentially overheating water). Samsung uses an NTC (Negative Temperature Coefficient) thermistor, meaning its resistance decreases as temperature rises. This is a different behavior than some other brands that use PTC sensors.

This repair is commonly needed when error 5E appears but the heating element itself tests normal (10-15 ohms). The thermistor is a much cheaper part ($15-$30) and easier to replace than the heating element, so testing it first saves time and money.

Before You Start

• Tools needed: Phillips #2 screwdriver, digital multimeter, flashlight, needle-nose pliers
• Parts needed: Samsung thermistor/temperature sensor (~$15-$30, model-specific)
• Time required: 20-30 minutes
• Difficulty: Intermediate
• Safety warning: Disconnect power at the circuit breaker. The thermistor operates on low voltage from the control board, but other components in the same area carry 120V AC. Always verify power is disconnected before reaching into the sump area.

How to Test the Thermistor

Before replacing, verify the thermistor has actually failed:

Test 1: Resistance at Room Temperature

1. Disconnect power at the breaker.
2. Remove the kick plate (two Phillips screws + two plastic clips).
3. Locate the thermistor. On Samsung dishwashers, it is a small probe mounted in the sump area near the heating element terminals. It has a two-wire connector leading to the control board.
4. Disconnect the thermistor's two-wire connector.
5. Set your multimeter to the 200K ohms range.
6. Measure resistance across the two thermistor pins.
7. At room temperature (approximately 77F/25C), a working Samsung NTC thermistor reads approximately 50,000 ohms (50K). Acceptable range is 40K-60K at room temperature.
8. If the reading is significantly outside this range (under 10K or over 200K, or open/OL), the thermistor has failed.

Test 2: Resistance Change with Temperature

If the room temperature reading is borderline, test temperature response:

1. With the thermistor disconnected, carefully heat the probe tip with a hair dryer for 30 seconds.
2. Measure resistance again immediately. It should have dropped significantly (to approximately 20-30K ohms).
3. A thermistor that reads the same regardless of temperature has failed internally and must be replaced.

Test 3: Continuity of Wiring

If the thermistor tests good but 5E still appears:

1. Set multimeter to continuity mode.
2. Test each wire from the thermistor connector back to the control board connector (may require tracing wires). A break in the wiring mimics a failed sensor to the control board.

Step-by-Step Replacement Instructions

Step 1: Disconnect Power

Turn off the circuit breaker for the dishwasher. Wait 2 minutes for any residual charge to dissipate.

Step 2: Remove the Kick Plate

Remove the two Phillips #2 screws on either side of the lower access panel. Release the two plastic squeeze clips at the top edge. Pull the panel forward and set aside.

Step 3: Locate the Thermistor

The thermistor is mounted in the sump housing area near the heating element terminals. It is a small cylindrical probe (about the size of a pencil eraser) inserted into the sump wall with a rubber grommet or plastic retaining clip. The probe tip extends into the water flow path inside the sump so it can measure actual water temperature. A two-wire connector leads from the probe body to the main wiring harness.

Step 4: Disconnect the Thermistor Wiring

Follow the two wires from the thermistor probe to their connector (usually within 6-8 inches of the probe). Press the locking tab and pull the connector apart. On some Samsung models, the wires lead directly to the control board with a connector at the board end. In that case, disconnect at whichever end is more accessible.

Step 5: Remove the Old Thermistor

The thermistor is held in place by one of these methods (depending on model):

• Rubber grommet mount: The probe pushes through a rubber grommet in the sump wall. Grip the probe body from the outside and pull straight out. The grommet may come with it or stay in the sump wall.
• Plastic clip mount: A plastic retaining clip holds the probe against the sump wall or in a mounting hole. Use a small flathead screwdriver to depress the clip tab and pull the probe free.
• Screw mount: Rarely, a single small screw holds a bracket that secures the probe. Remove the screw and slide the probe out.

Step 6: Inspect the Mounting Point

With the old thermistor removed, check the grommet or mounting hole for debris, mineral deposits, or damage. Clean if necessary. If using a rubber grommet that has hardened or cracked, the new thermistor may include a replacement grommet. If not, order one separately to prevent water leaking from the sump through the probe hole.

Step 7: Install the New Thermistor

Insert the new thermistor probe into the mounting hole:

• Grommet mount: Push the probe through the new or existing grommet until the probe tip extends into the sump interior by the same distance as the old one (typically 1/2 to 3/4 inch).
• Clip mount: Snap the new probe into the retaining clip until it clicks.
• Screw mount: Position and secure with the bracket screw.

Ensure the probe tip is in the water flow path. If it does not contact flowing water during operation, it will read ambient air temperature instead of water temperature, causing false 5E errors.

Step 8: Reconnect the Wiring

Plug the thermistor connector back together. Ensure the locking tab clicks. Route the wires away from the heating element terminals (heat from the element connections can damage thin sensor wires over time).

Step 9: Verify the Installation

Before reinstalling the kick plate, do a quick resistance check on the new thermistor through its connector to verify wiring integrity. You should read the same approximately 50K ohms as you measured on the new part alone.

Step 10: Test the Repair

Restore power at the breaker. Run a normal wash cycle. Monitor for error 5E. If using SmartThings, watch the temperature sensor reading during the cycle. It should show a steady temperature rise during the heating phase (from approximately 70F to 130-140F over several minutes). If the temperature reading rises normally and no error appears, the repair is successful.

Step 11: Reinstall the Kick Plate

Once confirmed working, reinstall the kick plate with its screws and clips.

Understanding Samsung NTC Thermistor Resistance Values

These are approximate values. Your exact readings may vary by 10-20% from these figures and still indicate a working sensor.

When to Call a Professional

• The thermistor tests good and the heating element tests good, but 5E persists (control board issue)
• You cannot locate the thermistor probe in the sump area (some models have it in non-obvious positions)
• The thermistor wiring is damaged or corroded inside the harness (requires harness repair or replacement)
• Water leaks from the thermistor mounting point after installation (grommet failure)

Cost Comparison: DIY vs Professional

Need Professional Help?

• Dishwasher repair service
• Samsung appliance repair
• Dishwasher repair cost guide

FAQ

Q: What is the difference between a thermistor and a thermostat in a Samsung dishwasher? A: A thermistor is a variable resistor that provides continuous temperature readings to the control board. A thermostat is a simple switch that opens or closes at a set temperature. Samsung dishwashers use thermistors (NTC type) for precise temperature control rather than fixed thermostats. This allows the control board to modulate heating precisely.

Q: Can a failing thermistor cause a Samsung dishwasher to overheat water? A: Yes. If the thermistor reads lower than actual temperature (resistance too high), the control board thinks water is cold and continues heating beyond the intended temperature. This can cause steam, extremely hot dishes, and potential damage to plastic components in the tub.

Q: Why does my Samsung dishwasher show 5E only on certain cycles? A: Different cycles heat to different temperatures. The Normal cycle heats to approximately 130F while Sanitize heats to 150F+. A thermistor that reads slightly off may pass the lower-temperature check but fail the higher one. This intermittent pattern confirms a degraded (not completely failed) thermistor.

Q: Do I need to calibrate the new Samsung thermistor after installation? A: No. Samsung NTC thermistors are passive components that do not require calibration. The control board reads the resistance value and converts it to temperature using a lookup table in its firmware. As long as the correct part number is installed, it works immediately.

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